Tetravalent metal acid triphosphates

ABSTRACT

This invention is based on the preparation of new solid acid triphosphates with compositions of the general formula M(IV)(HPO4)(H2PO4)2, where M(IV) is a tetravalent metal or a mixture of tetravalent metals. These compounds are insoluble in water the greater part of most organic solvents. They show a high non-water assisted protonic conductivity (about 0.01-0.04 S/cm at 100° C. and a relative humidity lower than 1%). These compounds can be used as proton conduction separators in electrochemical devices, to operate at low relative humidity values, as for example in different fuel cells, protonic pumps for electrochemical hydrogenation and dehydrogenation of organic compounds, or for hydrogen production from hydrogenated organic compounds by electro-reforming, or also for removing hydrogen from equilibrium reactions. These compounds can also be used in electrochemical sensors, in super capacitors and as acid catalysts in non-aqueous or anhydrous gaseous phases.

The invention relates to a metal acid phosphate composition of thegeneral formula M(IV)(HPO₄)(H₂PO₄)₂, methods for preparation, use of thecompositions and membranes and fuel cells comprising the composition.

The solid state protonic conduction phenomenon is of special interest,other than from a fundamental point of view, also for application inseveral electrochemical devices such as fuel cells for electric cars orother portable electric apparatus like cameras, computers, cellularphones and so on, protonic pumps, super capacitors for electric energystorage and so on.

The interest for hydrogen fuel cells has further grown up in the lastyears, following an increasing legislative control on atmosphericpollution in the most industrial countries.

Fuel cells use membranes possessing a high protonic conductivity and agood stability toward oxidation. Nowadays, preferred membranes are thosebased on sulphonated fluorocarbonic polymeric matrices, for exampleNafion™, which is developed and marketed by DuPont de Nemours, or otherperfluorinated acid membranes produced by the Dow Chemical Company,Solvay Solexis S.p.A. and Asahi Chemical Industry. These membranesgenerally have the required protonic conductivity and chemicalstability. However, they are very expensive for application in massproducts. Therefore, much effort has been done to develop protonicconduction membranes cheaper than the perfluorinated ones, such as thosebased on sulphonated polyetherketones or polysulphones. Unfortunatelythese last membranes do not show the excellent characteristics ofperfluorinated membranes. Furthermore, even when the economical aspectsof these protonic conductors could be positively solved, the large scalediffusion of cars using hydrogen as fuel is expected to be slowed downby the problems related to the refuelling for this gaseous fuel, and bythe real risks connected with the use of hydrogen. Market forecasts forhydrogen fuel cells to be used in portable electric devices are evenmore unfavourable. The use of liquid fuels, possibly with a lowinflammability, should make more easy the refuelling of cars at theexisting petrol pumps, and should reduce people wariness of this fuel.Therefore, Direct Methanol Fuel Cells (DMFCs), in which the cell isdirectly fed by a water solution of methanol, are currentlyinvestigated. Unfortunately, these cells have additional technologicalproblems, since all commercial membranes, including Nafion, show a muchtoo high permeability toward methanol. To solve this problem, currentDMFCs must operate with very dilute methanol solutions (1-2 molar).Moreover, even if the permeability toward methanol could be largelyreduced the use of more concentrated methanol solutions would bedifficult likewise, because the consequent reduction of water wouldconsiderably decrease the protonic conductivity of the membranes. Thisis due because, in all sulphonated polymer-based membranes, the protonictransport mechanism is assisted by water.

In the literature there are reported structural studies of trivalent Aland Sc triphosphate Al(H₂PO₄)₃ and Sc(H₂PO₄)₃ (D. Brodalla et al., Z.Natur-forsch., 36b, 907, 1981; Y. I. Sholin et al., KristallografiyaKRSA 27, 239, 1982). However, protonic conductivity measurementsperformed by us have shown that these trivalent aluminium and scandiumtriphosphates do not possess any appreciable protonic conductivity,especially at a low relative humidity.

For as concern solid state protonic conductivity in anhydrous conditionsliterature reports some membranes with an alkaline polymeric matrix, forexample those based on polybenzimidazole, that show an appreciableprotonic conductivity when they are charged with an excess amount ofsulphuric or phosphoric acid compared with the amount of polymeralkaline groups (J. C. Lassegues et al., Solid State Ionics, 145, 37,2001; D. J. Jones and J. Roziere, J. Membr. Sci., 185, 41, 2001).Unfortunately, these membranes tend to leak a considerable amount ofthese acids by and by, since they are very soluble both in water and inmany proton acceptor organic solvents. The recent compounds based onimidazole immobilized in an acidic polymeric matrix, described (M. F. H.Schuster et al., Solid State Ionics 145, 85, 2001) are more stable, buthave a still low protonic conductivity of about 0.001 S/cm.

The literature also reports acid salts of large monovalent cations, suchas RbHSO₄, CsHSO₄, and CsH₂PO₄, that show a non-water assisted protonicconductivity. These acid salts are known as “superprotonic phases”because they show a good conductivity (0.006-0.01 S/cm) only after aphase transition at 139° C. (A. I. Baranov et al., JEPT Lett. 36, 459,1982; F. E. G. Henn et al., Solid State Ionics 42, 29, 1990).

The invention is based on the object of providing new protonicconductors possessing a low methanol permeability and an acceptableprotonic conductivity even at low relative humidity values.

This object is achieved through the preparation of new protonicconductors based on tetravalent metal acid triphosphates with a protonicconductivity higher than that of the already known metal (IV)diphosphates with a layered structure, such as α-M(IV)(HPO₄)₂.H₂O andγ-M(IV)(PO₄)(H₂PO₄).2H₂O. New M(IV) acid triphosphates with athree-dimensional framework structure with compositionM(IV)(HPO₄)(H₂PO₄)₂ were prepared and surprisingly these acidtriphosphates have shown a very high protonic conductivity (about 0.03S/cm at 100° C.) even at very low relative humidity values (<1%). Thesenew M(IV) acid triphosphates have a non-water assisted protonicconduction mechanism different from previously known layereddiphosphates, and different from all sulphonated polymeric membranes.

The object of the invention is achieved through a metal acid phosphatecomposition of the general formula M(IV)(HPO₄)(H₂PO₄)₂ where M is atetravalent metal or a mixture of tetravalent metals. In the inventivemetal acid phosphate composition the ratio of metal atoms to phosphorousatoms is 1:3. Until now there are just compositions known with a metalto phosphorous ratio of 1:2.

Preferably, the proton conductivity of the inventive composition is atleast 0.001 S/cm and more preferably even more than 0.01 S/cm atsurroundings, that are substantially free from water. The above protonicconductivity is performed at a relative humidity of below 1% at 100° C.In general, the conductivity of the inventive metal acid triphosphatesis dependent not only on humidity but particularly on the temperature aswell. In a preferred embodiment the composition shows a protonicconductivity of at least 0.001 S/cm even in totally dry surroundings.

In a preferred embodiment the metal is at least one metal of the fourthgroup of transition metals. Preferably, the metal is at least one of thegroup consisting of titanium, zirconium and hafnium. It is alsopossible, that the metal is a metal of the fourth main group, preferablytin and lead, in particular in combination with at least one of thetransition metals, preferably titanium, zirconium and hafnium,especially with a content of up to 10% by weight of the metal of thefourth main group (0.5 to 10% by weight).

Preferably, the composition is insoluble in water at temperatures below8° C. In case of titanium, the metal acid triphosphate composition isstable in water up to 27° C. Further, the metal acid triphosphatecomposition is preferably stable in common organic solvents, especiallyalcohols, carbon tetrachloride, dimethylformamide and benzene attemperatures below 110° C.

The composition can have a three-dimensional trigonal structure.Preferably the M(IV) atoms are octahedrally coordinated with six oxygenatoms of adjacent acid phosphate groups. In particular, the O—O distancebetween two adjacent phosphate groups is below 3.0 Å, preferably below2.8 Å. It was found that in phosphates with an oxygen distance below 3.0Å a proton conduction free from water, originating directly from thephosphate protons, occurs, involving solely the adjacent phosphateprotons (see FIG. 5).

In one embodiment, the metal acid triphosphate composition, especiallywherein M is hafnium, is stable in air up to about 110° C. or more at awater vapour partial pressure below 7 mm Hg. In another embodiment,wherein M is titanium and zirconium, the composition is stable up toapproximately 100° C.

In one embodiment the density of the metal acid phosphate composition isin a range of 2 to 3.2 g/cm³, preferably ca. 2.5 g/cm³ in the case ofzirconium, preferably ca. 2.45 g/cm³ in the case of titanium and ca.3.11 g/cm³ in the case of hafnium.

In one embodiment the composition is proton-conductable in a polymer,that is non-proton conductable in a water-free state.

The M(IV) metal acid phosphate composition M(IV)(HPO₄)(H₂PO₄)₂ can beirreversible transferable into a M(IV) pyrophosphate M(IV)(P₂O₇) attemperatures above 110° C. Further, the composition can be reversibletransferable to M(IV) phosphate M(IV)(HPO₄)₂ at high humidities.

In a preferred embodiment the composition has a microcrystallinestructure. The crystal size of the composition can vary depending on thedifferent possible metal atoms and can range below 20 μm, preferablybelow 5 μm. In a preferred embodiment the crystal size is 10 μm,wherein. M is zirconium and about 5 μm wherein M is titanium. In case ofsurrounding polymers having insufficient conductivity in a state freefrom water, a regular particle structure of the M(IV) triphosphatecomposition is preferred to give an acceptable conductivity of an M(IV)triphosphate containing polymer composite.

The metal acid phosphate composition can exist in many different forms,particularly in the form of single component materials as well as in theform of composite materials. In one embodiment the composition has theform of a thin film. In another embodiment the composition has the formof a composite membrane. Advantageously, the composition in form of amembrane or a thin film is impermeable to methanol. The impermeabilityto methanol is of great importance for the application of the membraneor the thin film in direct methanol fuel cells (DMFC), hydrogen fuelcells or reformate fuel cells respectively. In still another embodimentthe composition has the form of a tablet. It is also possible that themetal acid triphosphate composition is embedded in a polymer, especiallyin a polymer membrane. Such polymer membranes comprising metal acidtriphosphate compositions can be used for example in fuel cells,electrolysis cells and in general for proton separating purposes in thegaseous and liquid phase.

Another object of the invention is a method for preparation of metalacid triphosphate compositions of the general formulaM(IV)(HPO₄)(H₂PO₄)₂ wherein M is a tetravalent metal or a mixture oftetravalent metals comprising the steps of treating a metal M(IV)containing material in phosphoric acid of at least 85% by weight,preferably in anhydrous phosphoric acid. The preferred phosphoric acidis ortho-phosphoric acid with a melting point of 42° C. which is atleast 14 molar. The phosphoric acid can either be a melted phosphoricacid or an anhydrous solution of phosphoric acid in an anhydrous organicor inorganic solvent. Further, the material is incubated at a highertemperature in the range of 70 to 100° C. followed by separating aM(IV)(HPO₄)(H₂PO₄)₂ containing material and the phosphoric acid.Separation of the material and the phosphoric acid in form of ananhydrous solution or a melt can be carried out for example bycentrifugation, filtration or by draining the phosphoric acid.Afterwards, the M(IV)(HPO₄)(H₂PO₄)₂ containing material optionally iswashed with an organic solvent that is able to dissolve phosphoric acid.Preferably, acetone or isopropanol is used for washing. Finally, it ispossible to dry the M(IV)(HPO₄)(H₂PO₄)₂ containing material attemperatures below decomposition temperature of the M(IV)(HPO₄)(H₂PO₄)₂composition. Therefore, temperatures below 100° C. are preferred fortitanium and zirconium whereas for hafnium the maximum temperature fordrying is about 110° C. Advantageously, a temperature in range from 50to 60° C. is applied for drying the M(IV)(HPO₄)(H₂PO₄)₂ containingmaterial.

In a preferred embodiment of the method of the invention for preparationof a M(IV)(HPO₄)(H₂PO₄)₂ containing material the metal M(IV) containingmaterial is a metal M(IV) containing compound. In case or a metal M(IV)containing compound the method for preparation comprises the followingsteps: at first the metal M(IV) containing compound is dispersed inphosphoric acid of at least 85%, preferably anhydrous, particularlymelted, phosphoric acid, followed by stirring the mixture at atemperature of 70 to 100° C. for some hours to 5 days. Preferably, themixture is stirred for 1 to 3 days followed by separating a preferablycrystalline solid of M(IV)(HPO₄)(H₂PO₄)₂ from the melt or solution ofphosphoric acid. Optionally it follows a washing of the preferablycrystalline solid M(IV)(HPO₄)(H₂PO₄)₂ with an organic solvent able todissolve phosphoric acid, preferably acetone or isopropanol.Advantageously the preferably crystalline solid M(IV)(HPO₄)(H₂PO₄)₂ isdried afterwards at a temperature below the decomposition temperature ofthe metal acid triphosphate M(IV)(HPO₄)(H₂PO₄)₂.

In another embodiment of the method according to the invention, themetal M(IV) containing material is a composite membrane containing ametal M(IV) compound. Preferably the M(IV) compound is at least one ofthe group of M(IV) propionate, M(IV) phosphate, M(IV) phosphonate.Preferably, the method according to the invention comprises treating aphosphoric acid stable membrane containing a metal M(IV) compound inphosphoric acid of at least 85%, preferably anhydrous, particularlymelted, phosphoric acid, followed by incubating the membrane attemperatures of 70 to 100° C. for 1 to 10, preferably 4 to 7 days.Finally, the membrane containing M(IV)(HPO₄)(H₂PO₄)₂ can be separatedfrom the melt or solution of phosphoric acid. Optionally, afterseparation, washing of the membrane containing M(IV)(HPO₄)(H₂PO₄)₂ withan organic solvent able to dissolve phosphoric acid, preferably acetoneor isopropanol, follows. Advantageously, the membrane containingM(IV)(HPO₄)(H₂PO₄)₂ is dried afterwards at a temperature below thedecomposition temperature of the metal acid triphosphateM(IV)(HPO₄)(H₂PO₄)₂.

In a preferred embodiment of the method the metal M(IV) containingcompound is at least one selected from the group of M(IV) metal powderor cuttings, dehydrated M(IV) phosphate of the formula M(IV)(HPO₄)₂,dehydrated M(IV) phosphonate, dehydrated M(IV) oxychloride anddehydrated M(IV) propionate. More preferably, titanium powder, zirconiumoxychloride. (ZrOCl₂), hafnium oxychloride, zirconium propionate andlayered or amorphous zirconium phosphate (Zr(HPO₄)₂).

Favourably, the anhydrous phosphoric acid is a solution of phosphoricacid prepared by dissolving anhydrous phosphoric acid in an anhydrousorganic solvent. Preferably, anhydrous phosphoric acid is dissolved inanhydrous isopropanol.

The invention also includes a composite membrane made of at least oneorganic polymer and at least one of a tetravalent metal acidtriphosphate M(IV)(HPO₄)(H₂PO₄)₂. It is possible that the compositemembrane comprises a single organic polymer as well as a compositemembrane comprising several organic polymers to achieve certaincharacteristics of the membrane material.

The invention further involves a composite membrane made of a porousmembrane wherein pores are filled with at least one of a tetravalentmetal acid phosphate of the general formula M(IV)(HPO₄)(H₂PO₄)₂ whereinM is a tetravalent metal or a mixture of tetravalent metals. In oneembodiment the membrane is an inorganic, preferably ceramic, membranewhereas in another embodiment of the invention the membrane is apolymeric porous membrane. It is possible to fill the porous membranedirectly with a metal acid triphosphate composition to obtain thecomposite membrane. Further on, the pores in the porous membrane can befilled initially with layered or amorphous phosphate, especially withzircon phosphate (Zr(HPO₄)₂), or alternatively with metal M(IV) followedby conversion of the metal or metal compound into the metal acidtriphosphate composition according to the invention. The size of theparticles within the pores of the porous membrane can vary from 1 to 10μm. The zircon containing compound Zr(HPO₄)(H₂PO₄)₂ preferably have aparticle size of 2 to 10 μm whereas the size of titanium containingcompound Ti(HPO₄)(H₂PO₄)₂ is ca. 1 μm.

The invention also includes a membrane for a protonic conductionseparator containing at least one of the tetravalent metal acidtriphosphates according to the invention. In a preferred embodiment theprotonic conduction separator membrane is a fuel cell membrane.

In a preferred embodiment the membranes according to the inventioncomprise a reinforcing element in form of supporting fabrics orsupporting membranes. These supporting elements can be made of fabrics,preferably of glass or of polymers.

The invention further comprises a thin layer that contains, preferablyconsists of, at least one preferably crystallized tetravalent metal acidtriphosphate according to the invention.

In one embodiment the metal acid triphosphate compositionM(IV)(HPO₄)(H₂PO₄)₂ can be compression-molded to a thin layer or pellet.

The invention further comprises a catalyst powder containing at leastone of the tetravalent metal acid triphosphates according to theinvention. The catalyst powder can be either heterogeneous orhomogeneous and can be used for hydrogenation, for acid catalysis and/orfor esterification.

Another subject of the invention is a super capacitor with twoconductors separated by a dielectric, wherein the dielectric containsand preferably consists of at least one of the tetravalent metal acidtriphosphates according to the invention. The super capacitor can beformed from a thin film or a pellet of the metal acid triphosphate.

Still another subject of the invention is a fuel cell containing atleast two particularly porous electrodes and a proton conducting thinlayer comprising at least one of the tetravalent metal acidtriphosphates according to the invention. Preferably, the fuel cell isone of the group consisting of direct methanol fuel cells (DMFC),hydrogen fuel cells (PEMFC) and reformate fuel cells. Reformate fuelcells use hydrogen that is in situ generated from biogas, natural gas,methane, propane, alcohols or from oil.

The invention comprises a fuel cell containing at least two electrodesand a proton conducting membrane according to the invention. Preferably,the fuel cell containing a proton conducting membrane is one of thegroup consisting of direct methanol fuel cells, hydrogen fuel cells andreformate fuel cells.

Another subject of the invention is a protonic pump with anode, cathodeand a proton conductive separator containing at least one of atetravalent metal acid triphosphate according to the invention.

An object of this invention is also the use of the metal acidtriphosphate composition according to the invention for preparation ofcomposite membranes containing organic polymers and the metal acidtriphosphate composition.

Another object of this invention is the use of the metal acidtriphosphate composition according to the invention for filling pores ofporous membranes. The membranes can be inorganic, preferably ceramic, orpolymeric membranes.

Another object of this invention is the use of the membranes accordingto the invention as a protonic conduction separator, preferably in fuelcells, particularly in direct methanol fuel cells (DMFC), hydrogen fuelcells (PEMFC) and reformate fuel cells. The membranes according to theinvention can also be used in other types of fuel cells. Further on, themembranes according to the invention can also be used as a protonicconduction separator in electrochemical sensors.

Still another object of the invention is the use of the metal acidtriphosphate composition according to the invention for preparation ofan isolator of super capacitors. Therefore, the composition can be usedas a pure thin film or as a pellet.

An object of the invention is also the use of the metal acidtriphosphate composition according to the invention as a heterogeneouscatalyst, preferably for anhydrous gas phase reaction, particularly foracid catalysis, hydrogenation or esterification reactions. Preferably,the composition is used in form of a powder as a heterogeneous orhomogeneous catalyst.

Another object of the invention is the use of the metal acidtriphosphate composition according to the invention as a thin layer onporous electrodes in a fuel cell, preferably in a direct methanol fuelcell, hydrogen fuel cell or reformate fuel cell. Further on, it ispossible to use the composition in other types of fuel cells.

An object of the invention is the use of the membranes according to theinvention in a fuel cell.

Another object of this invention is the use of the tetravalent metalacid triphosphates according to the invention in a protonic pump for theproduction or removal of gaseous hydrogen and for the electrochemicalcompression of hydrogen.

It should be pointed out that protonic conduction membranes with thesecharacteristics could induce the development of new protonic pumps ableto operate with anhydrous gas or in non aqueous liquid environments.Hydrogen production from hydrogenated organic compounds byelectrocatalytical deprotonation processes on these membranes could bealso possible. Materials showing a high protonic conductivity also innon aqueous environments should find application also in acid catalysisand electro catalysis in organic solvents and in electrochemicalsensors.

Compounds with this composition and properties can be obtained withtetravalent metals of the group consisting of zirconium, titanium andhafnium. Therefore, these new tetravalent metal acid triphosphates witha high non-water assisted protonic conductivity can be described by thegeneral formula M(IV)(HPO₄)(H₂PO₄)₂, where M(IV) is a tetravalent metalor a mixture of tetravalent metals.

To highlight oxygen atoms coordinated to the central tetravalent metalatom, the protonic conductors that are the object of this patent areformulated as M(IV)(O₂PO(OH))(O₂P(OH)₂)₂, where the oxygen atomscoordinated to the central metal atom are put on the left of thephosphorus atom.

It is assumed that this peculiar non-water assisted conductivity arisesfrom the presence of (O₂P(OH)₂) and (O₂PO(OH)) groups at the same time.(O₂PO(OH)) groups bear proton acceptor oxygen atoms, and play animportant role for the non-water assisted protonic conductivity. Thisfact should also explain why trivalent aluminium and scandium phosphatesdo not show a high protonic conductivity, even if they have similarstructure and composition.

The compounds object of this patent are the solids possessing thehighest protonic conductivity in the absence of water in the temperaturerange from 0 to 110° C. Furthermore, different from the above acid saltsof large monovalent cations, tetravalent metal acid triphosphates arevery insoluble in water and in the most common organic solvents. Thiscan prevent their dissolution when used in these liquids. Furthermoretetravalent metal acid triphosphate crystals are totally impermeable tomethanol, thanks to their compact three-dimensional structure.

One object of this invention is the preparation of tetravalent metalacid triphosphates with a three-dimensional structure, with compositionM(IV)(O₂PO(OH))(O₂P(OH)₂)₂, which are insoluble in water and/or in themost common organic solvents, which show a non-water assisted protonicconduction mechanism with a protonic conductivity not lower than 0.001S/cm, and preferably more than 0.01 S/cm, at 100° C. and relativehumidity <1%.

Another object of this invention is the use of the above compounds ascatalysts in heterogeneous acid catalysis in organic solvents or inanhydrous gaseous environments.

Another object of this invention is the use of the above compounds inthe form of thin films, pellets or composite membranes.

An object of this invention is also the use of the above thin films andcomposite membranes as protonic conduction separators in fuel cells, inparticular, in direct methanol fuel cells.

An object of this invention is also the use of the above thin films andcomposite membranes in electrochemical devices in which they are placed,as protonic conduction separators, between two porous catalyticelectrodes,

An object of this invention is also the use of the above thin films andcomposite membranes in protonic pumps operating under anhydrousconditions to make hydrogenation or de-hydrogenation reactions oforganic compounds, to eliminate gaseous hydrogen formed in equilibriumreactions or for hydrogen production from methanol or other hydrogenatedorganic compounds, by the application of an electric field between thetwo catalytic electrodes,

An object of this invention is also the use of the above thin films andcomposite membranes in electrochemical sensors to be used in anhydrousgaseous environments or organic liquids.

The independent and dependent Patent Claims are hereby incorporated intothe Description by way of reference.

Further features of the invention are apparent from the followingdescription of preferred embodiments and examples. The individualfeatures of the invention here may be realized alone or in combinationwith one another. The embodiments described serve for illustration andto improve understanding of the invention, and are in no way to beunderstood as limiting.

EXAMPLES Example 1

This example illustrates one method for the preparation of zirconiumacid triphosphate Zr(HPO₄)(H₂PO₄)₂ and reports some characteristics ofthis compound.

Zirconium oxychloride octahydrate, ZrOCl₂.8H₂O, is accurately dehydratedin an oven at 110° C. for about 1 h.

A weighed amount of anhydrous phosphoric acid (ortho-phosphoric acid,99%, p.a., Fluka), corresponding to 3 moles of this acid, is melted at atemperature between 70 and 90° C. A weighed amount of anhydrouszirconium oxychloride, corresponding to 0.1 moles of zirconium, isdispersed in this melt. This procedure has to be carried out with careunder a hood, because the formation of gaseous hydrochloric acid isobserved. After a few minutes zirconium oxychloride is completelydissolved in the melted phosphoric acid. The melt is left at the abovetemperature for about 48 h, preferably under stirring. During this time,a white microcrystalline solid precipitates. The solid is separated fromthe melt (for example by centrifugation or filtration) and is thenwashed with an anhydrous organic solvent, that is able to dissolvephosphoric acid, for example, acetone or iso-propanol.

The recovered solid has a density equal to 2.5 g/cm³ and a compositioncorresponding to the formula Zr(HPO₄)(H₂PO₄)₂. This solid shows a goodX-ray powder diffraction pattern (see FIG. 1), the values (in Å) of thefive more intense reflections of which are (in order of decreasingrelative intensity, reported in parentheses): 6.25 (1); 3.72 (0.8); 4.77(0.65); 2.97 (0.55); 3.45 (0.32). Structural studies have shown that thesolid has a three-dimensional framework structure and that zirconiumatoms are octahedrally coordinated.

This compound is insoluble in water but it was found to be stable onlyat temperatures below 8° C. In air, it was stable up to 100° C. but onlyat a water pressures below 7 mmHg, while at water pressures higher than7 mmHg, it converts into α-Zr(HPO₄)₂. At temperatures higher than about110° C. it converts into cubic zirconium pyrophosphate.

This compound is stable in common anhydrous organic solvents, such asalkanols, carbon tetrachloride, and benzene. In water/methanol mixtures,stability temperature ranges between 10 and 110° C., depending onmethanol molar fraction.

The protonic conductivity of this compound has been determined in a cellthat allows the measurement at different temperatures and relativehumidity values. This cell was previously described in G. Alberti etal., J. Membr. Sci. 185, 75-81, 2001. Conductivity values, determined at80, 90 and 100° C. and with a relative humidity lower than 1% are 0.02;0.024 and 0.03 S/cm, respectively.

Example 1bis

This example is a change of example 1, and specifically the amount ofzirconium oxychloride is replaced by an equivalent amount of anhydrouszirconyl propionate. In this case, evolution of gas is not observedbecause propionic acid remains dissolved in the melted phosphoric acid.For all the rest the procedure is analogous to that of example 1, andsimilar results are obtained.

Example 1tris

This example is a change of the method for the preparation of zirconiumacid triphosphate, Zr(HPO₄)(H₂PO₄)₂, which is illustrated in examples 1and 1bis, and specifically, layered α-Zr(HPO₄)₂.H₂O is used as zirconiumsource. A weighed amount of this last compound, corresponding to 0.1moles, is previously dehydrated at 110° C. for 1 h, and then added to 1mol of melted phosphoric acid at 85° C. X-ray diffraction patterns showthat a slow conversion from the layered compound to thethree-dimensional compound occurs, until full conversion (in about 4days). TABLE 1 Crystal data and refinement details for Zr(HPO₄)(H₂PO₄)₂Formula Zr(HPO₄)(H₂PO₄)₂ Formula weight 381.2  Crystal system trigonalSpace group R -3 c a (Å)      8.27325(3) b (Å)      8.27325(3) c (Å)    25.5433(2) α (°) 90  β (°) 90  γ (°) 120  V (Å³)   1514.12(1) Z 6d_(calc)(g/cm³)  2.51 Pattern range, 2θ (°) 20-139 No. of data 5949   Noof reflections 299  No. of refined parameters 36  R_(p)   0.084 R_(wp)  0.110 R_(F)2   0.103 χ  2.60

TABLE 2 Fractional atomic coordinates and isotropic displacementparameters for Zr(HPO₄)(H₂PO₄)₂ Atom x/a y/b z/c Uiso × 100 Zr(1) 0  0 01.46(2) P(2) 0.6686(3)  0 0.25 3.71(5) O(3) 0.5131(4) −0.1099(4)0.2123(1) 3.1(1) O(4) 0.7199(6) −0.1237(5) 0.2819(1) 7.5(2)

TABLE 3 Selected bond lengths and angles for Zr(HPO₄)(H₂PO₄)₂ bondlength (Å) Angle Amplitude (°) Zr(1)-O(3) 2.059(3) O(3)-Zr(1)-O(3) 91.1(1) P(2)-O(3) 1.496(3) O(3)-Zr(1)-O(3) 180 P(2)-O(4) 1.525(4)O(3)-Zr(1)-O(3)  88.9(1) O(4) • • • O(4) 2.408(7) O(3)-P(2)-O(3)112.5(3) (intra phosphate) O(4) • • • O(4) 2.770(7) O(3)-P(2)-O(4)112.3(2) (inter phosphate) O(4) • • • O(4) 2.750(7) O(3)-P(2)-O(4)107.7(2) (inter phosphate) O(4)-P(2)-O(4) 104.2(3) Zr(1)-O(3)-P(2)157.8(2)

Example 2

This example illustrates a method for the preparation of titanium acidtriphosphate, Ti(HPO₄)(H₂PO₄)₂, and reports same characteristics of thiscompound.

A weighed amount of powdered metallic titanium (Aldrich, grain sizelower than 27 mesh), corresponding to 0.1 moles of titanium is dispersedinto about 1.3 moles of melted anhydrous phosphoric acid at atemperature of 85° C. Metallic titanium is completely dissolved afterabout 1 h, giving a blue-violet clear solution. After some hours aviolet compound starts to precipitate, and, in the presence of air, awhite product with composition Ti(HPO₄)(H₂PO₄)₂ is obtained. The productis separated and washed according to example 1.

The recovered solid has a density equal to 2.45 g/cm³. This solid showsa good X-ray powder diffraction pattern, the values (in Å) of the fivemore intense reflections of which are (in order of decreasing relativeintensity, reported in parentheses): 3.59 (1); 6.04 (0.7); 2.88 (0.4);4.63 (0.3); 3.02 (0.3). Structural studies have shown that this solid isisostructural to that of the corresponding zirconium compound.

Titanium acid triphosphate was found to be stable at air at temperatureslower than about 100° C. and at water pressures lower than 27 mmHg. Itis insoluble and stable in methanol, other alkanols and common organicsolvents, such as carbon tetrachloride, dimethylformamide, benzene, etc.at temperatures lower than 110° C. In pure water this compound is stableat temperatures lower than about 27 to 28° C. In water/methanol mixturesits stability grows up from 27 to 100° C., as the molar fraction ofmethanol in the mixture increases. At temperatures higher than about110° C., condensation of phosphate to pyrophosphate groups occurs, whileat water pressures higher than about 27 to 30 mmHg, the conversion intothe layered α-Ti(HPO₄)₂.H₂O is observed.

Protonic conductivity, determined with the cell mentioned in example 1at temperatures of 90, 100, and 108° C. and at relative humidity lowerthan 1%, was 0.01, 0.012, and 0.014 S/cm, respectively.

Example 2bis

This example is a change of the method for the preparation of titaniumacid triphosphate, which is illustrated in example 2, and specificallythe reaction liquid, represented by the melted phosphoric acid, isreplaced by a solution of anhydrous phosphoric acid in anhydrousiso-propanol (3 moles of iso-propanol per mol of phosphoric acid). Forall the rest, the procedure is analogous to that of example 2, andsimilar results are obtained. TABLE 4 Crystal data and refinementdetails for Ti(HPO₄)(H₂PO₄)₂ Formula Ti(HPO₄)(H₂PO₄)₂ Formula weight337.88 Crystal system trigonal space group R -3 c a (Å)      7.97139(6)b (Å)      7.97139(6) c (Å)     24.9618(3) α (°) 90  β (°) 90  γ (°)120  V (Å³)   1373.64(2) Z 6 d_(calc)(g/cm³)  2.45 Pattern range, 2θ (°)12-138 No. of data 6300   No. of reflections 298  No. of refinedparameters 36  R_(p)   0.091 R_(wp)   0.124 R_(F)2   0.091 χ  3.33

TABLE 5 Fractional atomic coordinates and isotropic displacementparameters for Ti(HPO₄)(H₂PO₄)₂ Atom x/a (Å) y/b (Å) z/c (Å) Uiso · 100Ti(1) 0 0 0 1.71(5) P(2) 0.6521(2) 0 0.25 2.99(4) O(3) 0.1590(3)0.2221(3) 0.54478(8) 1.62(8) O(4) 0.5016(4) 0.4672(4) 0.5509(1) 5.6(1)

TABLE 6 Selected bond lengths and angles for Ti(HPO₄)(H₂PO₄)₂ bondLength (Å) Angle Amplitude (°) Tl(1)-O(3) 1.935(2) O(3)-Tl(1)-O(3) 89.98(9) P(2)-O(3) 1.485(2) O(3)-Tl(1)-O(3) 180 P(2)-O(4) 1.538(3)O(3)-Tl(1)-O(3)  90.02(9) O(4) • • • O(4) 2.459(5) O(3)-P(2)-O(3)112.1(2) (intra phosphate) O(4) • • • O(4) 2.797(4) O(3)-P(2)-O(4)107.8(1) (inter phosphate) O(4) • • • O(4) 2.595(5) O(3)-P(2)-O(4)111.5(1) (inter phosphate) O(4)-P(2)-O(4) 106.1(2) Tl(1)-O(3)-P(2)153.5(2)

Example 3

This example illustrates a method for the preparation of hafnium acidtriphosphate, Hf(HPO₄)(H₂PO₄)₂, and reports same characteristics of thiscompound.

Hafnium oxychloride octahydrate, (HfOCl₂.8H₂O, 98%, STREM CHEMICALS), isdehydrated in an oven at 110° C. for about 1 h.

A weighed amount of anhydrous phosphoric acid (Ortho-phosphoric acid,99%, p.a., FLUKA), corresponding to 1.5 moles of this acid, is melted at85 to 90° C. A weighed amount of anhydrous hafnium oxychloride,corresponding to 0.1 moles of hafnium is dispersed under stirring inthis melt. This procedure has to be carried out under a hood, asformation of gaseous hydrochloric acid is observed. The melt is left,preferably under stirring, for 3 to 4 days.

During this time, a white microcrystalline solid precipitates. The solidis separated from the melt (for example by centrifugation or filtration)and is then washed with an anhydrous organic solvent (e.g. acetone orisopropanol).

The recovered solid has density equal to 3.11 g/cm³ and a compositioncorresponding to the formula Hf(HPO₄)(H₂PO₄)₂. Its X-ray powerdiffraction pattern is shown in FIG. 6.

Structural studies have shown that the solid has a three-dimensionalframework structure similar to that of Zr(HPO₄)(H₂PO₄)₂.

Protonic conductivity, determined with the cell mentioned in example 1at temperatures of 80, 90, and 100° C. and at relative humidity lowerthan 1%, was 0.017, 0.02, and 0.024 S/cm, respectively.

Example 3bis

In contrast to zirconium acid phosphate, Hf(HPO₄)(H₂PO₄)₂ is lesssensitive to the presence of water. Therefore, this compound can also beprepared by using a solution of phosphoric acid 85% and/or HfOCl₂.8H₂O.A P/Hf molar ratio similar to that of example 2, and similar procedureof preparation were used. TABLE 7 Crystal data and refinement detailsfor Hf(HPO₄)(H₂PO₄)₂ Formula Hf(HPO₄)(H₂PO₄)₂ Formula weight 468.5 Crystal System Trigonal Space Group R-3c a (Å)      8.24968(3) c (Å)    25.4927(2) V (Å³)   1502.52(1) Z 6 d_(calc) (g/cm³)  3.11 Patternrange, 2θ(°) 16.5-139.4 No. of data 6144   No. of reflections 635  No ofrefined parameters 43  R_(p)   0.077 R_(wp)   0.100 R_(F)2   0.100 χ 2.91

TABLE 8 Atomic parameters and isotropic displacement factors forHf(HPO₄)(H₂PO₄)₂ Name x/a y/b z/c 100Uiso Hf1 0  0 0 2.04(2) P20.6662(5)  0 0.25 4.29(9) O3 0.4990(7) −0.1188(6) 0.2127(2) 3.6(2) O40.7199(8) −0.1237(9) 0.2867(3) 8.4(2)

TABLE 9 Selected bond distances and angles for Hf(HPO₄)(H₂PO₄)₂ BondLength (Å) Angle Amplitude (°) Hf1-O3 1.989(5) O3-Hf1-O3  88.8(2) P2-O31.555(5) O3-Hf1-O3 180 P2-O4 1.602(6) O3-Hf1-O3  91.2(2) O4 • • • O42.92(1) O3-P2-O3 110.2(4) (inter phosphate) O4 • • • O4 2.51(1) O3-P2-O4113.4(3) (inter phosphate) O3-P2-O4 106.5(3) O4-P2-O4 107.0(4) Hf1-O3-P2156.9(3)

Example 4

Preparation of a composite membrane material made ofPoly-2,2′-(m-phenylen)-5,5′-dibenzimidazole (PBI)/Zr(HPO₄)(H₂PO₄)₂ bytreatment of an α-zirconium phosphate containing composite membrane withmelted ortho-phosphoric acid at 80° C.

a) A 9% colloidal dispersion of an α-zirconium phosphate indimethylformamide is prepared according to PCT/EP 03/02550 (Example 1a).

b) High molecular weight Poly-2,2′-(m-phenylen)-5,5′-dibenzimidazole isprepared by extraction of commercial Polybenzimidazole Type Celazole®with dimethylformamide at 140° C. The resulting polymer should have aninherent viscosity of higher than 1.00 dl/g measured 0.5% H₂SO₄ at 30°C. The residue is dissolved in dimethylacetamide at 240° C. resulting 9%solution using an autoclave.

c) 25 g of a 9% solution of poly-2,2′(m-phenylen)-5,5′-dibenzimidazolein dimethylacetamide and 30 g of a 9% colloidal dispersion of anα-zirconium phosphate in dimethylformamide are mixed under vigorousstirring. The mixture is cast on a glass plate by means of an Erichsensemi automatic film casting processor. The solvent is removed by heating30 minutes at 110° C. and 5 hours at 140° C. The membrane thus obtainedafter delamination (thickness 30 μm) is slightly brownish.

d) The dry membrane is put into a reaction vessel containing meltedortho phosphoric acid at 80° C. The full conversion intoZr(HPO₄)(H₂PO₄)₂ takes place within 7 days. The treated membrane iswashed with acetone for complete removal of phosphoric acid.

Example 5

Preparation of a composite membrane material made ofPoly-2,5-benzimidazol (ABPBI)/Zr(HPO₄)(H₂PO₄)₂ by treatment of azirconyl propionate containing composite membrane with meltedortho-phosphoric acid at 80° C.

a) High molecular weight poly-2,5-benzimidazole is prepared during 2hours at 80° C. and 6 hours at 140° C. from 3,4-diaminobenzoic acid inEaton's reagent according to literature. The purified and powderedpolymer should have an inherent viscosity of higher than 5.00 dl/gmeasured in 0.2% H₂SO₄ at 30° C.

b) A 7% solution of ABPBI and 0.5% LiCl in N-Methylpyrrolidone isprepared at 260° C. with vigorous stirring, cooled down to 110° C. andfiltered. 15 g of zirconyl propionate are dissolved in 100 g of thesolution. The mixture is cast on a glass plate by means of an Erichsensemi automatic film casting processor. The solvent is removed by heating1 hour at 120° C. and 5 hours at 130° C. The membrane thus obtainedafter delamination (thickness 20 μm) is dark brown.

c) The dry membrane is put into a reaction vessel containing meltedortho phosphoric acid at 80° C. The full conversion intoZr(HPO₄)(H₂PO₄)₂ takes place within 7 days. The treated membrane iswashed with acetone for complete removal of phosphoric acid.

FIGURES

FIG. 1 shows an X-ray powder pattern of Zr(HPO₄)(H₂PO₄)₂

FIG. 2 shows a Rietveld plot for Zr(HPO₄)(H₂PO₄)₂

FIG. 3 shows a SEM picture of Zr(HPO₄)(H₂PO₄)₂ micro crystals.

FIG. 4 shows Ball and stick representation of the structure ofM(IV)(HPO₄)(H₂PO₄)₂

FIG. 5 shows a portion of the structure of Zr(HPO₄)(H₂PO₄)₂ in which thecontinuous H-bond path is represented as dashed lines

FIG. 6 shows an X-ray powder pattern of Ti(HPO₄)(H₂PO₄)₂

FIG. 7 shows a Rietveld plot for Ti(HPO₄)(H₂PO₄)₂

FIG. 8 shows a SEM picture of Ti(HPO₄)(H₂PO₄)₂ micro crystals.

FIG. 9 shows Rietveld plot for Hf(HPO₄)(H₂PO₄)₂

FIG. 10 shows the Arrhenius plot of Ti(HPO₄)(H₂PO₄)₂, Zr(HPO₄)(H₂PO₄)₂and Hf(HPO₄)(H₂PO₄)₂ and melted and solid H₃PO₄ for reference

FIG. 11 shows the thermo gravimetric-DTA curves for Zr(HPO₄)(H₂PO₄)₂

FIG. 12 shows the thermo gravimetric-DTA curves for Ti(HPO₄)(H₂PO₄)₂

FIG. 13 shows the stability curves of Ti(HPO₄)(H₂PO₄)₂, Zr(HPO₄)(H₂PO₄)₂and Hf(HPO₄)(H₂PO₄)₂

DATA COLLECTION, STRUCTURE SOLUTION AND REFINEMENT FOR Zr(HPO₄)(H₂PO₄)₂,Ti(HPO₄)(H₂PO₄)₂ AND Hf(HPO₄)(H₂PO₄)₂

X-ray powder diffraction patterns for structure determination andRietveld refinement were collected according to the step scanningprocedure with CuKα radiation on a Philips X'PERT APD diffractometer,PW3020 goniometer equipped with a bent graphite monochromator on thediffracted beam. 0.5° divergence and scatter slits and a 0.1 mmreceiving slit were used. The LFF ceramic tube operated at 40 KV, 30 mA.A first determination of cell parameters was made using the TREOR90program (P. E. Werner, L. Eriksson and M. Westdhal, J. Appl.Crystallogr., 1985, 18, 367). For this, a preliminary peak-profilefitting, using pseudo-Voigt functions for the determination of theposition of Kα₁ maxima, was carried out. The analysis of the indexedpatterns clearly revealed the presence of the following limitingreflection conditions: hkl, −h+k+l=3n which suggested a limited set ofprobable space groups. A systematic comparison of the number of peaksfound and the number of possible peaks, in all trigonal and hexagonalspace groups using the Chekcell program (J. Laugier and B. Bochu,LMGP-Suite, ENSP/Laboratoire des Matériaux et du Génie Physique, BP 46.38042 Saint Martin d'Hères, France) estimated R-3c as the best choice,for all structures.

The structures were solved by direct methods with the EXPO program (A.Altomare, M. C. Burla, G. Cascarano, C. Giacovazzo, A. Guagliardi, A. G.G. Moliterni and G. Polidori, J. Appl. Crystallogr., 1995, 28, 842.) andwere then refined with the GSAS program (A. Larson and R. B. Von Dreele,GSAS, Generalized Structure Analysis System, Los Alamos NationalLaboratory, 1988). All the atoms were refined isotropically and neutralatomic scattering factors were used. The shape of the profile wasmodelled by a pseudo-Voigt function in which a parameter for asymmetryat low angle was included. No correction was made for absorption. At theend of the refinement, the shifts in all parameters were less than theirstandard deviations.

Proton Conductivity

The measurements have been performed by impedance spectroscopy in thefrequency range 10 Hz-10 MHz at a signal amplitude <100 mV. TheSchlumberger 1260 Impedance/Gain Phase Analyser was used. The impedancedata were corrected for the contribution of the empty andshort-circuited cell. The pellet resistance was obtained byextrapolating the impedance data to the real axis on the high frequencyside.

Pellets, 10 mm in diameter and 1.5 to 1.7 mm thick, were prepared bypressing about 200 mg of material at 40 kN/cm². The two flat surfaces ofthe pellets were coated by a composite electrode consisting of a mixtureof platinum black (Ventron) with the material in the ratio 3:1.

A sealed-off cell, in which nitrogen can be fluxed, was used. In thetemperature range −23 to 80° C. pure nitrogen (relative humidity lowerthan 1%) was fluxed. In the temperature range 80 to 100° C. nitrogen wasfirst bubbled in water maintained with a thermostat at the suitabletemperature between 1 to 7° C. in order to have a relative humidity offluxed nitrogen of about 1% (this low humidity is necessary to avoidcondensation of the acid M(VI) acid triphosphates to pyrophosphates).

FIG. 10 shows the Arrhenius plot of Ti(HPO₄)(H₂PO₄)₂ andZr(HPO₄)(H₂PO₄)₂ in the temperature range 20 to 100° C. In the same FIG.10 is also reported the plot of Hf(HPO₄)(H₂PO₄)₂ determined in a largerrange of temperature (from −23° C. to 100° C.). As a comparison, theliterature data for molten and solid phosphoric acid are also reported.The activation energy for the conduction process in the temperaturerange 40 to 100° C. (obtained by the equation σT=Log·A−E_(a)/2.3RT) issimilar for all three materials (about 5.6 Kcal/mol).

Thermo Gravimetric Analysis

Thermo gravimetric (TG) and thermal differential analyses were performedwith NETZSCH 449C Thermoanalyser.

a) ZR(HPO₄)(H₂PO₄)₂

Zr(HPO₄)(H₂PO₄)₂ weight loss starts at about 180° C., with the loss ofabout 2.5 moles of water per mol of Zr, and the formation of cubic Zrpyrophosphate, according with the following reaction:Zr(HPO₄)(H₂PO₄)₂→ZrP₂O₇+0.5P₂O₅+2.5H₂O

A second loss, due to residual water and P₂O₅ sublimation starts atabout 450° C., and slowly continues up to 1200° C. At the end of theanalysis only TiP₂O₇ is present. The total weight loss is 29.14%(calculated: 30.43%). The FIG. 11 shows the thermo gravimetric-DTAcurves for Zr(HPO₄)(H₂PO₄)₂. Heating rate: 1° C./min. Air flow, 30ml/min.

b) Ti(HPO₄)(H₂PO₄)₂

Ti(HPO₄)(H₂PO₄)₂ weight loss starts at about 200° C., with the loss ofabout 2.5 moles of water per mol of Ti, and the formation of Tipyrophosphate, according with the following reaction:Ti(HPO₄)(H₂PO₄)₂→TiP₂O₇+0.5P₂O₅+2.5H₂O

A second loss, due to residual water and P₂O₅ sublimation starts atabout 500° C., and slowly continues up to 1200° C. At the end of theanalysis only ZrP₂O₇ is present. However, it is known that titaniumpyrophosphate starts to decompose over 1000° C. For this, thestoichiometry of the sample at the end of the analysis is unknown. FIG.12 shows the thermo gravimetric-DTA curves for Ti(HPO₄)(H₂PO₄)₂. Heatingrate: 1° C./min. Air flow, 30 ml/min.

Stability of M(IV)(HPO₄)(H₂PO₄)₂ Compounds

M(IV)(HPO₄)(H₂PO₄)₂ compounds are stable, under anhydrous conditions, upto about 100° C. At higher temperature, the transformation into cubiczirconium pyrophosphate, according to reaction:M(IV)(HPO₄)(H₂PO₄)₂→M(IV)P₂O₇+H₃PO₄+H₂O, takes place.

In presence of water, the release of phosphoric acid takes place attemperature lower than 100° C., with formation of the α-layeredstructure, according to the reaction:M(IV)(HPO₄)(H₂PO₄)₂+H₂O

M(IV)(HPO₄)₂.H₂O+H₃PO₄

It was found that this reaction is reversible.

It was of interest to see the stability of M(IV)(HPO₄)(H₂PO₄)₂ compoundsin methanol-water mixtures.

This stability was determined by dipping about 200 mg of sample in 10 mlof methanol-water at different fraction molar compositions andtemperature. After 7 days of contact, the samples were separated bycentrifugation and X-ray were taken. The sample was considered stablewhen its X-ray pattern was not changed and no peaks of other phases werepresent after this contact. Note that in all cases where instability wasfound, only the α-layered structure was formed under 100° C. Above 100°C., the cubic pyrophosphate M(IV)P₂O₇ was indeed found.

FIG. 13 shows the stability curves of Ti(HPO₄)(H₂PO₄)₂, Zr(HPO₄)(H₂PO₄)₂and Hf(HPO₄)(H₂PO₄)₂ (labelled as TiP3, ZrP3 and HfP3 respectively)compounds. The compounds can be considered stables, under the givenexperimental conditions, in all (T, X_(H2O)) points under the curve andinstable above the curve.

1. Metal acid phosphate composition of the general formulaM(IV)(HPO₄)(H₂PO₄)₂ where M is a tetravalent metal or a mixture oftetravalent metals.
 2. Composition according to claim 1, wherein thecomposition has a protonic conductivity of at least 0.001 S/cm,preferably more than 0.01 s/cm at surroundings substantially free fromwater.
 3. Composition according to claim 1, wherein M is at least onemetal of the fourth group of transition metals, preferably at least oneof the group consisting of titanium, zirconium and hafnium. 4.Composition according to claim 1, wherein the composition has athree-dimensional trigonal structure.
 5. Composition according to claim1, wherein M(IV) atoms are octahedrally coordinated with oxygen atoms ofacid phosphate groups.
 6. Composition according to claim 1, wherein aninter phosphate O—O distance of adjacent phosphate groups is below 3.0Å, preferably below 2.8 Å.
 7. Composition according to claim 1, whereinthe composition, especially wherein M is hafnium, is stable in air up toabout 100° C. or more at a water vapour partial pressures below 7 mm Hg.8. Composition according to claim 1, wherein the composition isprotonconductable in a polymer nonprotonconductable in a state free fromwater.
 9. Composition according to claim 1, wherein the composition hasa microcrystalline structure.
 10. Composition according to claim 9,wherein the composition has a crystal size of below 20 μm, preferablybelow 5 μm.
 11. Composition according to claim 1, wherein thecomposition has the form of a thin film.
 12. Composition according toclaim 1, wherein the composition has the form of a membrane. 13.Composition according to claim 1, wherein the composition has the formof a tablet.
 14. Composition according to claim 1, wherein thecomposition is embedded in a polymer membrane.
 15. A method forpreparation of compositions of the general structure M(IV)(HPO₄)(H₂PO₄)₂according to claim 1 based on the following steps: a) treating a metalM(IV) containing material in phosphoric acid of at least 85%, preferablyanhydrous, phosphoric acid b) incubating the material at a temperatureof 70-100° C., c) separating a M(IV)(HPO₄)(H₂PO₄)₂ containing materialand the phosphoric acid
 16. A method according to claim 15 wherein themetal M(IV) containing material is a metal M(IV) containing compound.17. A method according to claim 15 wherein the metal M(IV) containingmaterial is a membrane containing a metal M(IV) compound, preferably atleast one of the group consisting of M(IV) propionate, M(IV) phosphateand M(IV) phosphonate.
 18. Method according to claims 15, wherein theanhydrous phosphoric acid is a solution of phosphoric acid, prepared bydissolving anhydrous phosphoric acid in an anhydrous organic solvent,preferably isopropanol.
 19. Composite membrane made of organic polymersand at least one of a tetravalent metal acid triphosphate[M(IV)(HPO₄)(H₂PO₄)₂] according to claim
 1. 20. Composite membrane madeof a porous membrane wherein pores are filled with at least one of atetravalent metal acid triphosphate according to claim
 1. 21. Protonicconduction separator membrane containing at least one of the tetravalentmetal acid triphosphates according to claim
 1. 22. Thin layercontaining, preferably consisting of, at least one of a preferablycrystallized tetravalent metal acid triphosphate according to claim 1.23. Catalyst powder containing at least one of the tetravalent metalacid triphosphates according to claim
 1. 24. Super capacitor with twoconductors separated by a dielectric, wherein the dielectric contains,preferably consists of, at least one of the tetravalent metal acidtriphosphates according to claim
 1. 25. Fuel cell containing at leasttwo particularly porous electrodes and a proton conducting thin layercomprising at least one of the tetravalent metal acid triphosphatesaccording to claim
 1. 26. Fuel cell containing at least two electrodesand a proton conducting membrane according to claim
 19. 27. Protonicpump with an anode, a cathode and a proton conductive separatorcontaining at least one of a tetravalent metal acid triphosphateaccording to claim 1.